Visible light and ir combined image camera

ABSTRACT

Methods, camera, and a computer-readable medium for registering on a camera display infrared and visible light images of a target scene taken from different points of view causing a parallax error.

RELATED APPLICATIONS

The present application is a continuation of co-pending U.S. patentapplication Ser. No. 11/458,600, filed Jul. 19, 2006, which is acontinuation of U.S. patent application Ser. No. 11/294,752, filed Dec.5, 2005, now issued as U.S. Pat. No. 7,538,326, which in turn claimspriority to U.S. Provisional Patent Application No. 60/633,078, filedDec. 3, 2004, the disclosures of which are herein incorporated byreference in their entirety.

BACKGROUND

Many infrared cameras today produce an image (IR image) of a scene usingonly energy in the far-infrared portion of the electromagnetic spectrum,typically in the 8-14 micron range. Images obtained using these camerasassign colors or gray-levels to the pixels composing the scene based onthe intensity of the IR radiation reaching the camera's sensor elements.Because the resulting IR image is based on the target's temperature, andbecause the colors or levels displayed by the camera do not typicallycorrespond to the visible light colors of the scene, it can bedifficult, especially for novice users of such a device, to accuratelyrelate features of interest (e.g. hot spots) in the IR scene with theircorresponding locations in the visible-light scene viewed by theoperator. In applications where the infrared scene contrast is low,infrared-only images may be especially difficult to interpret.

An infrared scene is a result of thermal emission and, not all, but mostinfrared scenes are by their very nature less sharp compared to visibleimages which are a result of reflected visible light. For example,considering an electric control panel of an industrial machine which hasmany electrical components and interconnections, the visible image willbe sharp and clear due to the different colors and well defined shapes.The infrared image may appear less sharp due to the transfer of heatfrom the hot part or parts to adjacent parts.

When panning an area with an infrared camera looking for hot or coldspots, one can watch the camera display for a visible color change.However, sometimes the hot or cold spot may be small and the colorchange may go unnoticed. To aid in the identification of hot or coldspots, infrared cameras often indicate the hot spot or cold spotlocation via a visible cursor or other graphical indicator on thedisplay. The temperature of such hot spots, calculated using well-knownradiometric techniques (e.g., establishing or measuring a referencetemperature), is often displayed nearby the cursor. Even with the colorchange and the hot spot indications, it can be difficult to accuratelyrelate the hot spot (or other features of interest) in the cameradisplay's IR imagery with their corresponding locations in thevisible-light scene viewed by the operator.

To address this problem of better identifying temperature spots ofinterest, some cameras allow the operator to capture a visible-lightimage (often called a “control image”) of the scene using a separatevisible light camera built into the infrared camera. The FLIR ThermaCam®P65 commercially available from FLIR Systems of Wilsonville, Oreg. is anexample of such a camera. These cameras provide no capability toautomatically align, or to merge the visible-light and infrared imagesin the camera. It is left to the operator to manually correlate imagefeatures of interest in the infrared image with corresponding imagefeatures in the visible-light image.

Alternatively, some infrared cameras employ a laser pointer that iseither built into, or affixed to the camera. The FLIR ThermaCam® E65commercially available from FLIR Systems of Wilsonville, Oreg. is anexample of such a camera. This laser pointer projects a visible point orarea onto the target, to allow the user to visually identify thatportion of the target scene that is being displayed by the infraredcamera. Because the laser pointer radiation is in the visible spectrum,it is not visible in the infrared image. As a result, the laser pointeris of limited value in infrared cameras. This can be problematic whenthe location of a hot or cold spot is difficult to identify. Forexample, large industrial control panels often have many components thatare similar in shape and packed tightly together. It is sometimesdifficult to determine the exact component that is causing a thermalevent, such as a hot spot in the infrared camera image.

Other infrared temperature measurement instruments may employ either asingle temperature measurement sensor, or a very small number oftemperature sensors arrayed in a grid pattern. Single point instrumentstypically provide a laser pointing system to identify the target area byilluminating the point or area viewed by the single temperature sensorelement, e.g. Mikron M120 commercially available from Mikron InfraredInc. of Oakland, N.J. Alternatively, some systems employ an opticalsystem that allows the user to visually identify the point in the targetscene that is being measured by the instrument by sighting through anoptical path that is aligned with the temperature sensor, e.g. MikronM90 commercially available from Mikron Infrared Inc. of Oakland, N.J.Instruments with more than one sensor element typically provide a verycrude infrared image made up of a small number of scene pixels, eachwith a relatively large instantaneous field of view (IFOV), e.g. IRISYSIRI 1011 commercially available from Advanced Test Equipment of SanDiego, Calif. It can be very difficult to accurately identify featuresof interest using such images.

SUMMARY

Certain embodiments of the invention relate to a method of displayingvisible-light (VL) images and infrared (IR) images. The method includesproviding a camera having a VL lens with a VL sensor, an IR lens with anIR sensor, and display. The optical axes of the VL and IR lenses areoffset from and generally parallel to each other so that the VL and IRsensors sense VL and IR images, respectively, of a target scene fromdifferent points of view causing a parallax error. The method includesfocusing the IR lens on the target with the focusing operating to bringthe VL image into register with the IR image to correct the parallaxerror. The method also includes displaying at least a portion of the VLimage in register with at least a portion of the IR image on thedisplay.

Certain embodiments of the invention relate to a method of displayingvisible-light (VL) images and infrared (IR) images. The method includesproviding a camera having a VL lens with a VL sensor, an IR lens with anIR sensor, and display. The optical axes of the VL and IR lenses areoffset from and generally parallel to each other so that the VL and IRsensors sense VL and IR images, respectively, of a target scene fromdifferent points of view causing a parallax error. The method includesdisplaying at least a portion of the VL image with at least a portion ofthe IR image on the display where the IR image is displayed with thecorresponding portion of the VL image. The method also includesregistering the VL and IR images on the display by displacing themrelative to each other until registered to correct the parallax errorvia a manual adjustment mechanism.

Certain embodiments of the invention relate to a camera that producesvisible light (VL) and infrared (IR) images. The camera includes a VLlens, a VL sensor, an IR lens, an IR sensor, and a display. The VLsensor is associated with the VL lens and has an array of VL sensorelements that produce a VL image of a target scene. The IR sensor isassociated with the IR lens and has an array of IR sensor elements thatproduce an IR image of the target scene. The IR image is produced bysubstantially fewer sensor elements than are used to produce the VLimage. The optical axes of the VL and IR lenses are offset from andgenerally parallel to each other so that the VL and IR sensors sense VLand IR images, respectively, of a target scene from different points ofview causing a parallax error. Rotation of the IR lens causes an axialshift of the IR lens relative to the IR to the IR sensor to focus the IRlens. The focusing of the IR lens registers the VL image with the IRimage to correct the parallax error. The display concurrently displaysat least a portion of the VL image registered with at least a portion ofthe IR image.

Certain embodiments of the invention relate to a computer-readablemedium programmed with instructions for performing a method ofregistering multiple images where the medium comprising instructions forcausing a programmable processor to receive first and second images of atarget scene. The first image is produced by a VL lens and a VL sensorwith an array of VL sensor elements. The second image has a parallaxerror with the first image and is produced by an IR lens and an IRsensor with an array of IR sensor elements. The IR sensor hassubstantially fewer sensor elements than the VL sensor. The medium alsoincludes instructions to determine a value indicative of the distancebetween the IR lens and a target within the target scene. The mediumalso includes instructions to correct the parallax error using thedetermined value to register the first and second images, and display atleast portions of the first and second images on a display with theportions of the first and second images in register.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are front and rear perspective views of a camera accordingto an embodiment of the invention.

FIG. 3 shows a block diagram of a representative camera system accordingto an embodiment of the invention that can be used to practiceembodiments of the invention.

FIG. 4 is a diagram showing the optical path and sensor configuration ofthe camera.

FIG. 5 shows geometrically, the derivation of the parallax equation.

FIG. 6 shows the (Full-Screen, Full-Sensor infrared)/(Full-Screen,Partial-Sensor Visible-Light) scene display mode.

FIGS. 7 and 8 are cross-sectional views of an infrared camera modulewith a magnet and Hall-Effect sensor according to an embodiment of theinvention.

FIG. 9 shows combined visible-light and infrared images uncorrected forparallax error.

FIG. 10 shows the same images corrected for parallax error.

FIG. 11 shows the (Partial-Screen, Partial-Sensorinfrared)/(Full-Screen, Full-Sensor Visible-Light) scene display mode.In this mode, the camera uses all of the visible-light sensor elementsto fill the display.

FIG. 12 shows the (Partial-Screen, Full-Sensor infrared)/(Full-Screen,Partial-Sensor Visible-Light) scene display mode. In this mode, thecamera uses all of the available infrared sensor elements to provide aninfrared image that fills only a central area of the camera display.

FIG. 13 shows the (Partial-Screen, Full-Sensor infrared)/(Full-Screen,Full-Sensor Visible-Light) scene display mode. In this mode, the camerauses all of the infrared and all of the visible-light sensor elements toconstruct the displayed images.

FIGS. 14-16 show respectively, an infrared only image of an insulatedcup, a visible-light only image of the cup and a partial alpha-blendedimage of the cup.

FIG. 17 shows an example of a “hot threshold” alarm mode display.

FIG. 18 shows a typical infrared image of a low infrared contrast scene.

FIG. 19 shows the same scene with an alpha-blended visible-light image,yielding a much higher apparent contrast.

FIGS. 20-23 show, respectively, a visible-light image with a laser spot,a visible-light image with the laser spot and a computer generated lasermarker aligned with the laser spot, an infrared only image with thecomputer generated laser marker and hot spot not aligned, and aninfrared only image with the computer generated laser marker and hotspot aligned.

FIGS. 24-26 show, respectively, a visible-light only image with a laserpoint, an alpha-blended visible-light/infrared image with a laser pointand hot spot not aligned, and an alpha-blended visible-light/infraredimage with a laser point spot aligned.

FIGS. 27-28 show, respectively, an infrared only image with a computergenerated laser pointer and hot spot not aligned and an infrared onlyimage with the computer generated laser pointer and hot spot aligned.

FIGS. 29-30 show, respectively, a visible-light only image with a laserspot and a computer generated laser marker not aligned and avisible-light only image with the laser spot and computer generatedlaser marker aligned.

DETAILED DESCRIPTION System Description

FIGS. 1 and 2 are perspective views of the front and the back of acamera 10 according to an embodiment of the invention. The housingincludes an infrared camera module and a visible-light camera module. Inparticular, the camera 10 includes a camera housing 12, a Visible-Light(VL) lens 13, an infrared lens 14, focus ring 16 and a laser pointer 18as well as various electronics located within the housing as will bedescribed with reference to FIG. 3. In an embodiment, an LED torch/flash17 is located on each side of the VL lens 13 to aid in providing enoughlight in dark environments. A display 20 is located on the back of thecamera so that infrared images, visible light images and/or blendedimages of Infrared and Visible-Light may be viewed. In addition, targetsite temperature (including temperature measurement spot size) anddistance readings may be displayed. Also located on the back of thecamera are user controls 22 to control the display mode and activate ordeactivate the laser pointer.

FIG. 3 shows a block diagram of a representative camera system accordingto an embodiment of the invention that can be used to practiceembodiments of the invention.

The Visible-Light camera module includes a CMOS, CCD or other types ofvisible-light camera, LED torch/flash and a laser pointer. This camerastreams RGB image display data (e.g. 30 Hz) to the FPGA for combinationwith infrared RGB image data and then sends the combined image data tothe display.

The Analog Engine interfaces with and controls the infrared sensor, andstreams raw infrared image data (e.g. 30 Hz) to the DSP. The DSPperforms computations to convert the raw infrared image data to scenetemperatures, and then to RGB colors corresponding to the scenetemperatures and selected color palette. For example, U.S. Pat. No.6,444,983 entitled “Microbolometer Focal Plane Array With ControlledBias,” assigned to the present assignee, is incorporated herein in itsentirety, discloses such an infrared camera. The DSP then streams theresulting infrared RGB image display data to the FPGA where it iscombined with the VL RGB image data and then sends the combined imagedata to the display.

The Embedded Processor Card Engine includes a general-purposemicroprocessor that provides a graphical user interface (GUI) to thecamera operator. This GUI interface consists of menus, text, andgraphical display elements that are sent to the FPGA, where they arebuffered in SRAM and then sent to the display.

The MSP430 interfaces with the user interface including camera buttons,mouse, LCD backlight, and the smart battery. It reads these inputs andprovides the information to the embedded processor card engine where itis used to control the GUI and provides other system control functions.

The FPGA drives the display(s) (LCD and/or TV, for example) withcombined visible-light image data, infrared image data, and GUI data.The FPGA requests both the visible-light and infrared image data fromthe VL and infrared camera modules and alpha-blends them together. Italso alpha-blends the resulting display image with the GUI data tocreate a final blended image that is sent to the LCD display. Of coursethe display associated with the embodiments of the invention is notlimited to an LCD-type display. The FPGA operates under control of theDSP, which is further controlled by the embedded processor card engine.The degree of image alpha-blending and the display mode, i.e.picture-in-a-picture, full screen, color alarm and zoom mode, iscontrolled by the user through the GUI. These settings are sent from theembedded processor card engine to the DSP which then configures the FPGAproperly.

Optical Configuration

Embodiments of the invention combine an engine of a real-timevisible-light camera with an engine of a real-time infrared camera closeto each other in the same housing such that the optical axes are roughlyparallel to each other.

The camera according to the embodiments of the invention places theengine or module of a real-time visible-light camera in the housing of areal-time infrared camera. The placement is such that the visible andinfrared optical axes are as close as practical and roughly parallel toeach other, for example, in the vertical plane of the infrared opticalaxis. Of course other spatial arrangements are possible. The visiblelight camera module, i.e., VL optics and VL sensor array, are chosen tohave a larger field of view (FOV) than the infrared camera module. FIG.4 is a diagram showing the optical path and sensor configuration of thecamera. As shown in the diagram, there are two distinct optical pathsand two separate sensors. One for visible-light, and one for infrared.Because the optical paths for the sensors are different, each sensorwill “see” the target scene from slightly different vantage pointsthereby resulting in parallax error. As will be described in detailhereinafter, the parallax error is corrected electronically usingsoftware manipulations. This provides the capability to electronicallycorrect the displayed images for parallax. In certain embodiments, thevisible-light optics and sensor are chosen so that their respectivefield of views (FOV) are different, i.e. one is larger than the other.For instance, in one embodiment, the VL FOV is greater than the infraredFOV. This provides cost effectiveness. Presently, for a given number ofpixel sensors, visible light sensor arrays are much cheaper thaninfrared sensor arrays. Accordingly, for a given field of view andresolution (instantaneous field of view), visible light sensor arraysare cheaper than infrared sensor arrays.

In certain embodiments, the visible light optics are such that thevisible light camera module remains in focus at all usable distances.Only the infrared lens needs focus adjustment for targets at differentdistances.

Parallax Correction and Display Modes

FIG. 5 shows geometrically, the derivation of the parallax equation (eq.1). As can be seen by the equation, parallax can be reduced byminimizing the distance (q) between the visible-light and infraredoptical apertures, and also by choosing short focal length lenses. Thecamera design will typically physically fix (q). In certain embodiments,the focal lengths of the visible-light and infrared lens (f) can bealtered in the field by changing lenses, or using optical systems thatinclude multiple focal lengths or continuous zoom. In the embodimentswith fixed focal length lenses, the focal lengths remain constant duringoperation once the lenses are installed. Hence, during camera operation,parallax is simply a function of distance (d) to the target. In theembodiment shown, the focal length (f) of each lens is the same. Inalternate embodiments, the focal lengths (f) of the infrared lens andthe visible lens may differ from each other.

The camera corrects the visible-light and infrared images for parallaxand provides several different methods to display the registered imagesto the operator. These methods are described below. In general, parallaxerror corrections are based on the infrared focus distance as will bedescribed hereinafter. However, parallax error may also be corrected bydetermining the distance from the target image (other than via focusdistance) by schemes known to those of ordinary skill in the art.

The camera according to the embodiments of the invention can operate inone of three display modes; 1) full screen visible, infrared and/orblended, 2) picture-in-a-picture such as partial infrared image in afull screen visible image, and 3) infrared color alarms in visible-lightimages. In any one of these display modes, temperatures will be recordedand can be displayed in the infrared portion of the image. Temperaturescan also be displayed on a visible-light only image from the recordedbut not displayed infrared image.

In the full screen display mode, an operator has a choice of selectingfor display a full screen visible-light only image, a full screeninfrared only image, or a full screen blend of visible-light andinfrared images. In an embodiment of the invention, the display is about320 by 240 pixels and is represented by the dashed-line box shown inFIG. 6. The infrared sensor has 160 by 120 pixels and the visible-lightsensor has 1280 by 1024 pixels. These particular dimensions are given byway of example and are not limiting to any of the embodiments of theinvention. Thus, the infrared sensor, the VL sensor and display may eachbe individually larger or smaller than the particular examples given.FIG. 6 shows a diagram of the mode where the full 160 by 120 infraredimage is interpolated to fill the camera display. Based on the displaymode chosen, a portion of the 1280 by 1024 visible-light image iswindowed to match the infrared window. Since the number of selectedvisible-light sensor elements does not necessarily match the 320 by 240pixels of the camera display, the visible-light image is scaled to matchthe camera display. After parallax error correction, each resultinginfrared display pixel will represent the same instantaneous field ofview (IFOV) as its corresponding visible-light display pixel. Becausethe two images are matched, the camera operator can easily identifypoints-of-interest in the infrared image with objects in thevisible-light image simply by noting where the features of interestoverlie each other in the two images. In the embodiment shown in FIG. 6,the display mode is entitled “Full-Screen, Full-Sensor Infrared andFull-Screen, Partial-Sensor Visible-Light display mode.” Additionaldisplay modes are discussed further below.

Parallax error between the visible-light image and the infrared image iscorrected automatically by the camera. This process is referred to asregistering. In order to apply the proper parallax correction, thecamera must first determine the distance to the target object ofinterest. One method to determine the target distance is to sense thefocus position of the infrared lens using a Hall-effect sensor. FIGS. 7and 8 show a sectional view of camera 10 taken from front to rearthrough the center of infrared lens 14. Referring to FIGS. 7 and 8, aHall-Effect sensor 30 is fixed in the housing 32 with respect to theinfrared sensor array 34 to sense the proximity of a magnet 36 attachedto the back of the IR lens 14. As the focus of the lens is changed viarotation of focus ring 16, the distance f′ between the magnet 36 and theHall-Effect sensor 30 changes, resulting in an output from theHall-Effect sensor that is proportional to focus position. (The focus ofthe lens could be changed by moving the lens or moving the infraredsensor array.) This focus position is used to derive an estimate of thedistance to the target. The infrared lens focus position provides anespecially convenient estimate of distance because typical infraredlenses have a low F-number, resulting in a shallow depth of field. TheHall-Effect sensor may, in one embodiment, be fixed on the infraredsensor array. In addition, the positions of the Hall-Effect sensor andmagnet may be reversed from that shown.

In the embodiment shown in FIGS. 7 and 8, the magnet 36 is a ring thatencircles an interior surface of the focus ring 16 facing the infraredsensor array 34. The Hall-Effect sensor 30 is fixed in the camerahousing 32 a small distance from of the infrared sensor array 34. Thedistance between the Hall-Effect sensor and the magnet represents thedistance f′ shown in FIGS. 7 and 8. FIG. 7 shows the lens positioned fornear focus and FIG. 8 shows the lens positioned for far focus in whichcase the magnet is closer to the Hall-Effect sensor than in FIG. 7.Mechanisms and methods other than those described above for a Halleffect sensor may, of course, be employed to determine the distance totarget. Such equivalent mechanisms or methods would be known to thosewith skill in the art. The Hall-Effect sensor is one convenient method.

Estimating the distance between the target and the camera is a valuablesafety feature. For example, OSHA has specific safety distancerequirements when inspecting high voltage electrical cabinets. Thus,using the camera according to the embodiments of the invention, one candisplay the distance to the target on the display so that the cameraoperator is assisted in complying with OSHA's safety requirements.

In addition, it can be valuable to know the size of the spot on thetarget that is being measured (instantaneous field of view spot size).Because the spot size is a function of distance and the embodiments ofthe invention have the ability to measure (or rather estimate) distancethat is needed to correct parallax error, spot size can be calculated asa function of distance and displayed to the camera operator via thedisplay.

The lens position sensor value to focus distance correlation for eachinfrared lens is determined at the factory and stored with other cameracalibration data in the camera's non-volatile memory. This calibrationdata includes X and Y image offsets calculated for each focus distance.By utilizing the sensed infrared lens focus position and the factorycalibration data, the correct X and Y sensor offsets of the partial areafrom the visible-light sensor to be displayed can be computed and usedto select the appropriate visible-light sensor area for the currentinfrared focus distance. That is, as the focus distance of the infraredlens is changed, different areas of the visible-light sensor image areextracted and displayed, resulting in registration of the infrared andvisible-light images for objects at the focus distance. FIG. 9 showscombined picture-in-a-picture display of visible-light and infraredimages misaligned, i.e. uncorrected for parallax error. FIG. 10 showsthe same images corrected for parallax error. Referring to FIG. 9, thecenter quarter of the display shows a blurry (unfocused) andunregistered infrared-only image 40 placed within the surroundingframework of a visible only image 42. The rectangular dark sections 44in the image are misaligned (unregistered) showing the parallax errorresulting from the unfocused infrared image 44. Referring to FIG. 10,the rectangular dark sections 44 in the infrared image 40 are registeredwith the portions of such sections 44 in the visible only image 42,showing that infrared image is now properly focused. FIGS. 9 and 10highlight a method by which a user of camera 10 could focus the infraredimage 40 by merely rotating focus ring 16 until image 40 is properlyregistered. Although FIGS. 9 and 10 show the center quarter of thedisplay as infrared only, this same method and technique could be usedfor a blended visible and infrared image, whether the images are shownpicture in picture, full display, alarm mode, or other display modes.

Note that objects within the scene that are not at the focus distancewill still exhibit a parallax error. Nearer objects will exhibit alarger parallax error than objects beyond the focus distance. Inpractice, parallax error becomes negligible beyond a focus distance ofapproximately 8 feet for lenses used with typical infrared cameras. Alsonote that parallax errors can only be corrected down to a limited closefocus distance to the camera (typically about 2 feet). This distance isdetermined by how much “extra” field of view the visible-light sensorprovides as compared to the infrared sensor.

When an image is captured, the full visible-light image and the fullinfrared image with all of the ancillary data are saved in an image fileon the camera memory card. That part of the visible-light image notdisplayed which lies outside of the camera display dimensions when theimage was taken is saved as part of the visible-light image. Later, ifan adjustment in the registration between the infrared and visible-lightimage is needed, either in the camera or on a computer, the fullvisible-light image is available.

The camera allows the operator to adjust the registration of thevisible-light and infrared image after an infrared/Visible-light imagepair is captured and stored in memory. One way to accomplish this is touse the infrared lens position as an input control. This allows theoperator to fine-tune the registration, or to manually register objectsin the scene that were not at the infrared focus distance when theimages were captured, simply by rotating the focus ring on the lens.

The visible-light image, when it is the only displayed image, isdisplayed preferably in color, although it need not be. When it isblended with the infrared image, the visible-light image is converted togray scale before it is blended so that it only adds intensity to thecolored infrared image.

FIG. 11 shows the scene display mode entitled “Partial-Screen,Full-Sensor Infrared and Full-Screen, Partial-Sensor Visible-Lightdisplay mode.” In this mode, the camera uses all of the availableinfrared sensor elements to provide an infrared image that fills only acentral area of the camera display. Standard image processing techniques(e.g. scaling and windowing, for example) are used to fit the infraredimage into the desired area of the display. The IFOV of thevisible-light image is adjusted to match the IFOV of the infrared imageand then a portion of the visible-light image is selected to fill thefull display and to match the infrared image in the center of thedisplay. The center quarter of the display can be infrared only,visible-light only or a blend of the two. The remaining three-quartersof the display (outer framework) is visible-light only.

The camera uses the same technique in this mode as that described forthe full screen mode to correct for parallax.

Alternatively, instead of matching the visible-light image to theinfrared image just the opposite may be done. FIGS. 12 and 13 illustratethis technique. FIG. 12 shows a picture-in-a-picture “Partial-Screen,Partial-Sensor infrared and Full-Screen, Full-Sensor Visible-Light scenedisplay mode.” In this mode, the camera uses all of the visible-lightsensor elements to fill the display. If the number of visible-lightsensor elements does not match the number of display pixels, the camerauses standard imaging techniques to create an image that fills thedisplay screen. A portion of the available infrared sensors is chosen toprovide the infrared image. The infrared image is windowed and matchedso that the resulting infrared display pixels provide the same IFOV asthe visible-light image display pixels.

The camera uses similar techniques to those described for FIG. 6 tocorrect for parallax. However, in this mode, different areas of theinfrared sensor are selected to match the center region of thevisible-light image as the infrared focus distance is changed. Note thatin this mode, the infrared image is always displayed in a fixed positionin the middle of the display.

FIG. 13 shows the “Partial-Screen, Full-Sensor infrared and Full-Screen,Full-Sensor Visible-Light scene display mode.” In this mode, the camerauses all of the infrared and all of the visible-light sensor elements toconstruct the displayed images. The visible-light image is scaled tocompletely fill the display. The infrared image is windowed and scaledso that the IFOV of the resulting display pixels match the visible-lightimage. The resulting image is displayed over the matching area of thevisible-light image.

Like the previously described mode, parallax is corrected by moving theinfrared image scene to align it with the visible-light image scene.

Alpha-Blending

Alpha-blending is a process of rationing the transparency/opaqueness oftwo images superimposed on one pixel. If the Alpha=maximum, then thefirst image is opaque and the second is transparent and is so written tothe display. If Alpha=0, then the first image is transparent and thesecond image is opaque and is so written to the display. Valuesin-between cause ‘blending’ (alpha blending) between the two sources,with the formula Display=Source 1*(Alpha/max_Alpha)+Source2*((max_Alpha-Alpha)/max_Alpha).

FIGS. 14-16, show respectively, an infrared only image of an insulatedcup, a visible light (VL) only image of the cup, and a partialalpha-blending of the infrared and VL images.

The camera will enable the operator to adjust the alpha blending of thevisible and infrared images from the extremes of infrared-only (FIG. 14)or visible-only (FIG. 15) to any combination of alpha blending betweenthese two extremes (FIG. 16). Note that although the infrared image isnot visible in FIG. 15, the underlying infrared image data is used todisplay the correct object temperature 52 in the visible light image.Thus, as the cursor is moved over the visible-light image, thetemperature 52 associated with the cursor's location on the image isdisplayed.

The infrared and visible-light images can be displayed in either coloror grayscale. When color is used to portray temperatures in the infraredimage, the visible image in the overlap area can be displayed ingrayscale only so that it doesn't excessively corrupt the infraredpalette colors.

When an image is saved, both the visible and infrared images are savedindividually so reconstructing images with different alpha blending canbe accomplished later either in the camera, or with PC software.

Alarm Modes

The camera supports several different visual alarm modes. These modesare used to call the operator's attention to areas of interest in thevisible-light image by displaying an alpha-blended or infrared onlyimage in areas that meet the alarm criteria as set by the user. FIG. 17shows an example of the “hot threshold” alarm mode. Only those pixels inthe infrared image that exceed a set temperature threshold (hotspots 60)are displayed. In the color alarm mode, the visible-light image 62 isswitched to gray scale so that the infrared image stands out with noambiguity. The camera can provide alarm modes, such as those describedbelow. Other alarm modes are also possible.

-   -   Absolute hot threshold—infrared pixels above a defined        temperature are alpha-blended with corresponding visible-image        pixels.    -   Absolute cold threshold—infrared pixels below a defined        temperature are alpha-blended with corresponding visible-image        pixels.    -   Relative hot threshold—A temperature range is defined by the        user. The temperature range is relative to the current hottest        pixel (or average of a set number of hottest pixels) in the        scene or from a previous scene or reference scene. Infrared        pixels above the threshold defined by the current hottest        pixel(s) in the scene minus a user defined or predetermined        temperature range are alpha-blended with their corresponding        visible-image pixels. For example, if the temperature range is 5        degrees, and the current hottest pixel(s) in the scene is 100        degrees, for example, all infrared pixels above 95 degrees in        the scene will be alpha-blended with corresponding visible-light        pixels.    -   Relative cold threshold—A temperature range is defined by the        user. The temperature range is relative to the current coldest        pixel (or average of a set number of coldest pixels) in the        scene or from a previous scene or reference scene. Infrared        pixels below the threshold defined by the current coldest        pixel(s) in the scene plus a user defined or predetermined        temperature range are alpha-blended with their corresponding        visible-image pixels. For example, if the temperature range is 5        degrees, and the current coldest pixel(s) in the scene is 10        degrees, all infrared pixels below 15 degrees in the scene will        be alpha-blended with corresponding visible-light pixels.    -   Absolute range (isotherm)—The operator enters a temperature        range. Infrared pixels with a temperature within the set range        are alpha-blended with their corresponding visible-light pixels.        For example, the user enters a range of 80-100 degrees. All        infrared pixels with a temperature value within the 80-100        degree range are alpha-blended.    -   Alarm flash mode —To further call attention to areas of        interest, the camera may provide a mode whereby the        alpha-blended areas are “flashed” by alternately displaying the        alarmed pixels as visible-light only, and then either        alpha-blended or infrared only.

The alarm modes identified above may also be indicated audibly or viavibration. Such audible or vibrational alarms may be useful insituations where hotspots are small enough to otherwise go unnoticed inthe visual display. In embodiments that include audible or vibrationalarms, the camera can generate such an alarm to alert the cameraoperator when, for instance, the camera detects an out of specificationtemperature or any of the other alarms modes identified above. Referringback to FIG. 3, the camera may include an alarm module connected to theFPGA that provides audible or vibrational alarms. The vibrationmechanism can be similar to that used in cellular phones to alertpersons of an incoming call.

PC Software

All of the image display techniques described for the camera can also beimplemented in software that runs on a PC host computer and can beapplied to images captured by the camera.

ADVANTAGES

The advantages have already been stated above. The infrared image willnot only be sharper with much more detail, it will be surrounded with avisual image showing exactly what and where the infrared targets are.Parallax error will be automatically corrected, yielding a visible-lightcontrol image that is correctly registered with the infrared image.Infrared cameras can be made with smaller less expensive detectorarrays, yet display the apparent detail and contrast of very expensiveinfrared cameras with large and ultra-sensitive detector arrays. FIG. 18shows a typical infrared image of a low infrared contrast scene. FIG. 19shows the same scene with an alpha-blended visible-light image, yieldinga much higher apparent contrast with target site temperaturemeasurement.

Uses

This camera can be used in all phases of infrared thermography wherecurrent infrared cameras are used today and in the future. In the caseof the simplest uses such as an electricians tool, the camera can bemade inexpensively with a small infrared detector array and yet havevery high performance—high image quality with high spatial resolutionand accurate temperature. In the case of high-end thermography thecamera can be made at a lower cost and have images with greater apparentdetail than the most expensive infrared cameras. The camera willeliminate the need to take separate visible-light images to be includedin thermography reports.

Laser Pointer

Various applications are possible using the laser embodiments of thepresent invention. As previously mentioned, because the laser pointerradiation is in the visible spectrum, it is not visible in the infraredimage. As a result, the laser pointer is of limited value in infraredcameras. This is problematic when the location of a hot or cold spot isdifficult to identify. For example, large industrial control panelsoften have many components that are similar in shape and packed tightlytogether. It is sometimes difficult to determine the exact componentthat is causing a hot spot in the infrared camera image. In addition, inbuilding inspection applications where a wall appears uniform in thevisible image but shows a defect in the infrared image, the laserpointer of the embodiments of the invention can be used to identify theexact location of the defect on the wall. For roof leak detectionapplications, it can greatly aid the thermographer in marking the areasuspected of needing repair. The camera operator can outline the wetarea by adjusting the camera pointing so that the laser spot seen in theimage outlines the suspected wet area in the image and thus alsooutlines the suspected wet area on the roof with the laser beam so thatit can be correctly marked. In an R&D application where the target iscomplex such as a printed wiring board assembly, the laser pointerembodiments of the invention may aid in identifying the location of theinfrared point of interest.

The laser pointer of the embodiments of the invention is used toaccurately identify the location of infrared points-of-interest and toeasily aid the focusing of the infrared optics. FIGS. 24-26 show anassociated sequence of events. The laser pointer can be turned on usingone of the camera's programmable buttons or by other mechanisms by thecamera operator. At a reasonable distance, the laser pointer spot 100 onthe target can be seen in the visible-light image (FIG. 24) and in theblended visible-light and infrared image that has been corrected forparallax error (FIG. 25). Once the laser spot is identified in theblended image (FIG. 25), the camera operator can adjust the camerapointing until the laser spot in the blended image matches the spot ofinterest 102 in the infrared image (FIG. 26). The laser beam then marksthe target at the point-of-interest (FIG. 26).

Because the camera according to the embodiments of the invention hasbeen calibrated in the factory to identify the location of the laserspot in the infrared image using parallax calibration data as a functionof infrared camera module focus distance, the camera operator does notneed to see displayed the laser spot in the VL image. If the target isat a distance and/or has a low reflection for the laser wavelength, thelaser spot may be too weak for the VL camera to show prominently on thecamera display but it can still be seen on the target by the humanobserver. FIGS. 27 and 28 show an associated sequence of events. In thiscase, the infrared focus is adjusted as normally done by observing thesharpness of the infrared image. A computer-generated laser spotreference mark 200 is registered with the infrared image so that arepresentative mark (e.g., circle) is displayed on the infrared image(FIG. 27). The camera operator then adjusts the camera pointing untilthe laser calibration mark 200 lies over the infrared point-of-interest202 (FIG. 28). Once that happens, the laser beam then strikes the targetat the point of interest.

Alternatively, the camera operator first focuses the infrared imageusing an infrared display image only, switches to the visible-lightdisplay where the laser 210 will be shown in the display as seen in FIG.20. The operator marks the laser spot 210 on the display with a marking212 such as a circle (see FIG. 21) and then switches the display back tothe infrared only (see FIG. 22) where the marking 212 is registered withthe infrared image and it is displayed on the infrared image, positionedin the center quarter of the display area. The operator then adjusts thecamera pointing so that the mark 212 on the infrared display matches thethermal spot of interest 214 on the infrared display. (see FIG. 23) Oncethat happens, the laser beam then strikes the target at the point ofinterest.

Using the Laser Pointer to Focus the Infrared Image

With calibration data correcting for parallax between the laser pointerand the infrared image and the ability to see the actual laser spot inthe VL image, a process for monitoring and aiding the infrared focus ispossible. FIGS. 29 and 30 show an associated sequence of events. In thiscase, the location of the laser spot 220 is visible in the VL image(FIG. 29). The camera according to the embodiments of the invention hasbeen calibrated in the factory to generate a computer-generated laserspot reference mark 222 that indicates the location of the laser spot ina focused infrared image using parallax calibration data as a functionof infrared camera module focus distance. This reference mark may bedisplayed in the IR image or the VL image (that overlaps the IR image).In FIG. 29, the reference mark 222 is shown in the VL only image. As theinfrared lens is adjusted, the mark moves in the VL image showing thespot where the laser dot would be in the infrared image. When theinfrared mark is coincident with the laser dot seen in the VL image(FIG. 30), the focus adjustment may stop and the infrared camera moduleis in focus. This allows the most novice operator to focus the infraredlens and eliminates the subjective nature of focusing.

1. A method of displaying visible-light (VL) images and infrared (IR)images, the method comprising: providing a camera having a VL lens witha VL sensor, an IR lens with an IR sensor, and a display, the VL lensand the IR lens being located on the camera such that an optical axis ofthe VL lens is offset from, and generally parallel to, an optical axisof the IR lens so the VL sensor and the IR sensor sense a VL image andan IR image, respectively, of a target scene from different points ofview causing a parallax error; focusing the IR lens on the target scene,with the focusing of the IR lens operating to bring the VL image intoregister with the IR image to correct the parallax error; and displayingat least a portion of the VL image in register with at least a portionof the IR image on the display.
 2. The method of claim 1, wherein theportion of the IR image is displayed without displaying a correspondingportion of the VL image.
 3. The method of claim 1, wherein the portionof the VL image is displayed without displaying a corresponding portionof the IR image.
 4. The method of claim 1, wherein the portion of the IRimage is blended with a corresponding portion of the VL image.
 5. Themethod of claim 1, wherein the portion of the IR image is surrounded bythe portion of the VL image to effect a picture-in-picture view of thetarget scene.
 6. The method of claim 5, wherein the portion of the IRimage is blended with a corresponding portion of the VL image.
 7. Themethod of claim 1, wherein the VL sensor includes an array of VL sensorelements and the IR sensor includes an array of IR sensor elements, theIR image being formed by substantially fewer sensor elements than beingused to form the VL image.
 8. The method of claim 1, wherein the VLsensor includes an array of VL sensor elements, and wherein the at leastthe portion of the VL image is formed from fewer than all of the VLsensor elements.
 9. The method of claim 1, wherein the IR sensorincludes an array of IR sensor elements, and wherein the at least theportion of the IR image is formed from all of the IR sensor elements.10. The method of claim 9, wherein the at least the portion of the IRimage fills only part of the display, the part of the display beinggenerally centrally located on the display.
 11. The method of claim 10,wherein the at least the portion of the VL image fills the remainder ofthe display not filled by the at least the portion of the IR image,whereby the target scene is displayed in a picture-in-picture view. 12.The method of claim 11, wherein the at least the portion of the VL imagefills the entire display, the portion of the IR image being blended witha corresponding portion of the VL image, whereby the target scene isdisplayed in a picture-in-picture view.
 13. The method of claim 1,wherein the at least the portion of the IR image fills the entiredisplay.
 14. The method of claim 1, wherein focusing the IR lens on thetarget scene comprises moving the IR lens with respect to the IR sensor.15. The method of claim 1, wherein the focusing the IR lens is manual.16. The method of claim 1, further including sensing the IR lens focusposition, the IR lens focus position being used to bring the VL imageinto register with the IR image.
 17. The method of claim 16, furtherincluding determining the distance to the target scene based on the IRlens focus position.
 18. The method of claim 1, further includingreading a lens position sensor to sense the IR lens focus position. 19.A method of displaying visible-light (VL) images and infrared (IR)images, the method comprising: providing a camera having a VL lens witha VL sensor, an IR lens with an IR sensor, and a display, the VL lensand the IR lens being located on the camera such that an optical axis ofthe VL lens is offset from, and generally parallel to, an optical axisof the IR lens so the VL sensor and the IR sensor sense a VL image andan IR image, respectively, of a target scene from different points ofview causing a parallax error; displaying at least a portion of the VLimage with at least a portion of the IR image on the display, the atleast the portion of the IR image being displayed without thecorresponding portion of the VL image; and registering the VL image withthe IR image on the display by displacing the VL image and the IR imagerelative to each other until registered to correct the parallax errorvia a manual adjustment mechanism.
 20. The method of claim 19, whereinthe IR image has a smaller field of view than the VL image and the atleast the portion of the IR image is surrounded by the at least theportion of the VL image to effect a picture-in-picture view of thetarget scene.
 21. The method of claim 19, wherein the VL sensor includesan array of VL sensor elements and the IR sensor includes an array of IRsensor elements, the IR image being formed by substantially fewer sensorelements than being used to form the VL image.
 22. The method of claim19, wherein the VL sensor includes an array of VL sensor elements, andwherein the at least the portion of the VL image is formed from fewerthan all of the VL sensor elements, the IR sensor including an array ofIR sensor elements, and the at least the portion of the IR image isformed from all of the IR sensor elements.
 23. The method of claim 19,wherein the at least the portion of the IR image fills only part of thedisplay, the part of the display being generally centrally located onthe display, the at least the portion of the VL image fills theremainder of the display not filled by the at least the portion of theIR image, whereby the target scene is displayed in a picture-in-pictureview.
 24. A camera producing visible light (VL) and infrared (IR)images, the camera comprising: a VL lens; a VL sensor associated withthe VL lens and having an array of VL sensor elements that produce a VLimage of a target scene; an IR lens; an IR sensor associated with the IRlens and having an array of IR sensor elements that produce an IR imageof the target scene, the IR image being formed by substantially fewersensor elements than being used to form the VL image, the IR lens beingrotatable, rotation of the IR lens causing an axial shift of the IR lensrelative to the IR sensor to focus the IR lens; the VL lens and the IRlens being located on the camera such that an optical axis of the VLlens is offset from, and generally parallel to, an optical axis of theIR lens so the VL sensor array of pixels and the IR sensor array ofpixels sense the target scene from different points of view causing aparallax error, the focusing of the IR lens registering the VL imagewith the IR image to correct the parallax error; and a display forconcurrently displaying at least a portion of the VL image registeredwith at least a portion of the IR image.
 25. The camera of claim 24,wherein the portion of the IR image is displayed without displaying acorresponding portion of the VL image.
 26. The camera of claim 24,wherein the portion of the VL image is displayed without displaying acorresponding portion of the IR image.
 27. The camera of claim 24,wherein the portion of the IR image is blended with a correspondingportion of the VL image.
 28. The method of claim 24, wherein the VL lenswith the VL sensor has a larger field of view than the IR lens with theIR sensor.
 29. The camera of claim 28, wherein the displayed portion ofthe IR image is surrounded by the VL image to effect apicture-in-picture view of the target scene.
 30. The camera of claim 24,wherein the at least the portion of the IR image fills only part of thedisplay, the part of the display being generally centrally located onthe display, the at least the portion of the VL image fills theremainder of the display not filled by the at least the portion of theIR image, whereby the target scene is displayed in a picture-in-pictureview.
 31. The camera of claim 24, wherein the at least the portion ofthe VL image is formed from fewer than all of the VL sensor elements,and the at least the portion of the IR image is formed from all of theIR sensor elements.
 32. The camera of claim 24, further including asensor that determines a value indicative of the axial distance betweenthe IR lens and the IR sensor, the value being used to register the VLimage with the IR image to correct the parallax error.
 33. The camera ofclaim 32, wherein the value indicative of the axial distance provides avalue indicative of the distance to the target scene.
 34. The camera ofclaim 24, wherein the IR lens is manually rotatable.
 35. Acomputer-readable medium programmed with instructions for performing amethod of registering multiple images, the medium comprisinginstructions for causing a programmable processor to: receive a firstimage of a target scene, the first image being produced by a VL lens anda VL sensor with an array of VL sensor elements; receive a second imageof the target scene, the second image having a parallax error with thefirst image and being produced by an IR lens and an IR sensor with anarray of IR sensor elements, the IR sensor having substantially fewersensor elements than the VL sensor; determine a value indicative of thedistance between the IR lens and a target within the target scene;correct the parallax error using the determined value to register thefirst and second images; and display at least portions of the first andsecond images on a display with the portions of the first and secondimages in register.
 36. The computer-readable medium of claim 35,wherein the value indicative of the distance between the IR lens and thetarget is an IR lens focus position.
 37. The computer-readable medium ofclaim 35, wherein the portion of the second image is displayed withoutdisplaying a corresponding portion of the first image.
 38. Thecomputer-readable medium of claim 35, wherein the portion of the firstimage is displayed without displaying a corresponding portion of thesecond image.
 39. The computer-readable medium of claim 35, wherein theportion of the second image is blended with a corresponding portion ofthe first image.
 40. The computer-readable medium of claim 35, whereinthe at least the portion of the VL image is formed from fewer than allof the VL sensor elements, and the at least the portion of the IR imageis formed from all of the IR sensor elements.
 41. The computer-readablemedium of claim 35, wherein the VL lens with the VL sensor has a largerfield of view than the IR lens with the IR sensor, and the displayedportion of the second image is surrounded by the first image to effect apicture-in-picture view of the target scene.
 42. The computer-readablemedium of claim 35, wherein the at least the portion of the second imagefills only part of the display, the part of the display being generallycentrally located on the display, the at least the portion of the firstimage fills the remainder of the display not filled by the at least theportion of the second image, whereby the target scene is displayed in apicture-in-picture view.
 43. The computer-readable medium of claim 35,wherein the value indicative of the distance between the IR lens and thetarget is the distance between the IR lens and the target.
 44. Thecomputer-readable medium of claim 43, further comprising display thedistance between the IR lens and the target.
 45. The computer-readablemedium of claim 35, further comprising receive a sensed focus positionof the IR lens.
 46. The computer-readable medium of claim 45, whereinthe value indicative of the distance between the IR lens and the targetis based on the sensed IR lens focus position.
 47. The computer-readablemedium of claim 45, wherein the sensed IR lens focus position isreceived from a lens position sensor.